Add support for PCRE marks

Hi internals! I wrote a patch to expose PCRE mark information in PHP, see https://github.com/php/php-src/pull/609/files. The last passed *MARK will be added to the $matches array under key "MARK". If you don't use marks everything stays exactly the same. Does anyone have a problem with exposing it in this way? In this context, would there be a problem with increasing the minimum required PCRE version (for builds against an external library) from 6.6 to 8.10 (the current, bundled version is 8.34)? That would avoid adding #ifdefs for this code. Is there some particular reason for 6.6 here? Thanks, Nikita